Spring Boot Actuator - MAX property

Question

I am using Spring Boot Actuator dependency to get insights of application. For that, I have used Spring Boot Admin. Configuration for client-server is working fine. I have to measure the count, total-time, max for endpoints which are going to execute.

uri:/user/asset/getAllAssets
TOTAL_TIME: 831ms
MAX: 0ms 

uri:/user/getEmployee/{employeeId}
TOTAL_TIME: 98ms
MAX: 0ms

Why MAX (time) is 0 while TOTAL_TIME: is Xms

While I execute generalize form

localhost:8889/actuator/metrics/http.server.requests I get the MAX as 3.00..

I had also seen production-ready-features but not able to find any description about how MAX is calculated or what does it represent

Notes: with the number of request in an increase, COUNT, TOTAL_TIME is also getting an increase but MAX is reducing sometimes (see Request 1, Request 2 for details)

Request 1: http.server.requests

 {
        "name": "http.server.requests",
        "description": null,
        "baseUnit": "seconds",
        "measurements": [
            {
                "statistic": "COUNT",
                "value": 597
            },
            {
                "statistic": "TOTAL_TIME",
                "value": 144.9057076
            },
            {
                "statistic": "MAX",
                "value": 3.0002913
            }
        ],
        "availableTags": [
            {
                "tag": "exception",
                "values": [
                    "None"
                ]
            },
            {
                "tag": "method",
                "values": [
                    "GET"
                ]
            },
            {
                "tag": "uri",
                "values": [
                    "/actuator/metrics/{requiredMetricName}",
                    "/**/favicon.ico",
                    "/actuator",
                    "/user/getEmployee/{employeeId}",
                    "/user/asset/getAllAssets",
                    "/actuator/health",
                    "/actuator/info",
                    "/actuator/env/{toMatch}",
                    "/actuator/metrics",
                    "/**"
                ]
            },
            {
                "tag": "outcome",
                "values": [
                    "CLIENT_ERROR",
                    "SUCCESS"
                ]
            },
            {
                "tag": "status",
                "values": [
                    "404",
                    "200"
                ]
            }
        ]
    }

---

UPDATE

localhost:8889/actuator/metrics/http.server.requests?tag=uri:/user/getEmployee/2

Response 404 (I have executed /user/getEmployee/2 before making a request for actuator)

---

localhost:8889/actuator/metrics/http.server.requests?tag=uri:/user/getEmployee/{employeeId}

Response 400

---

localhost:8889/actuator/metrics/http.server.requests?tag=uri:/user/asset/getAllAssets

{
    "name": "http.server.requests",
    "description": null,
    "baseUnit": "seconds",
    "measurements": [
        {
            "statistic": "COUNT",
            "value": 1
        },
        {
            "statistic": "TOTAL_TIME",
            "value": 0.8311609
        },
        {
            "statistic": "MAX",
            "value": 0
        }
    ],
    "availableTags": [
        {
            "tag": "exception",
            "values": [
                "None"
            ]
        },
        {
            "tag": "method",
            "values": [
                "GET"
            ]
        },
        {
            "tag": "outcome",
            "values": [
                "SUCCESS"
            ]
        },
        {
            "tag": "status",
            "values": [
                "200"
            ]
        }
    ]
}

Request 2: http.server.requests

localhost:8889/actuator/metrics/http.server.requests

{
    "name": "http.server.requests",
    "description": null,
    "baseUnit": "seconds",
    "measurements": [
        {
            "statistic": "COUNT",
            "value": 3346
        },
        {
            "statistic": "TOTAL_TIME",
            "value": 559.7992767999998
        },
        {
            "statistic": "MAX",
            "value": 2.3612968
        }
    ],

Answer 1

• What does MAX represent

MAX represents the maximum time taken to execute endpoint.

Analysis for /user/asset/getAllAssets

COUNT  TOTAL_TIME  MAX
5      115         17
6      122         17  (Execution Time = 122 - 115 = 17)
7      131         17  (Execution Time = 131 - 122 = 17)
8      187         56  (Execution Time = 187 - 131 = 56)  
9      204         56  From Now MAX will be 56 (Execution Time = 204 - 187 = 17)  

---

• Will MAX be 0 if we have less number of request (or 1 request) to the particular endpoint?

No number of request for particular endPoint does not affect the MAX

---

• When MAX will be 0

There is Timer which set the value 0. When the endpoint is not being called or executed for sometime Timer sets MAX to 0. Here approximate timer value is 2.30 minutes (150 seconds)

---

• How I have determined the timer value?

For that, I have taken 6 samples (executed the same endpoint for 6 times). For that, I have determined the time difference between the time of calling the endpoint - time for when MAX set back to zero

DistributionStatisticConfig has .expiry(Duration.ofMinutes(2)).bufferLength(3) which sets some measurements to 0 if there is no request has been made in between expiry time or rotate time.

---

MAX property belongs to enum Statistic which is used by Measurement (In Measurement we get COUNT, TOTAL_TIME, MAX)

public static final Statistic MAX

The maximum amount recorded. When this represents a time, it is reported in the monitoring system's base unit of time.

---

Notes: This is the cases from metric for a particular endpoint (here /actuator/metrics/http.server.requests?tag=uri:/user/asset/getAllAssets).

For generalize metric of actuator/metrics/http.server.requests

As you can see from Request 1, Request 2 (in question) the MAX has been reduced (from 3.0002913 to 2.3612968) so that maybe because of MAX for some endPoint will be set backed to 0 due to a timer. In my view for MAX for /http.server.requests will be same as a particular endpoint. (but sure on that, investigating on it)